As optical communication networks employing wavelength division multiplexing (WDM) become increasingly pervasive, a new line of optical performance monitors, including spectral power monitors, is in demand.
Conventional spectral power monitors in the art typically use a wavelength-dispersing means, such as a diffraction grating or a dispersing prism, to separate a multi-wavelength optical signal into a spatial array of spectral channels with distinct center wavelengths. An array of photo-detectors (e.g., photodiodes) is positioned to detect the spectral channels individually, thereby providing an optical power spectrum of the multi-wavelength optical signal. Alternatively, a rotating diffraction grating and a stationary photo-detector, or a movable photo-detector and a stationary diffraction grating, are used to scan the spectral channels sequentially. These prior spectral power monitors are typically high in cost, cumbersome in size and operation, and in some instances require considerable maintenance, rendering them unsuitable for optical networking applications.
Moreover, the diffraction efficiency of a diffraction grating is known to be characteristically polarization sensitive. Such polarization sensitivity may be particularly acute for high-dispersion diffraction gratings (e.g., holographic gratings), which are desired for providing enhanced spectral resolution in spectral power monitors.
In view of the foregoing, there is a need in the art for optical spectral power monitors that overcome the shortcomings of the prior devices in a simple, effective, and economical construction.